Amplifier control circuit



March 29, 1949. R. W. LAVENDER 2,465,809

AMPLIFIER CONTROL CIRCUIT Filed oct. 1s, 194,6 2 sheets-sheet 1 GP/D SIG/VAL 'riga Irwvento': Raymond VV. Lavande?,

. v voL maf ,47 rfa/WML /5 i r/M.r

March 29, 1949. R. W.,LAVENDER 2,465,809

AMPLIFIER CONTROL CIRCUIT Filed Oct. 18A, 1946 2 Sheets-Sheet 2 l 27 cmo van/165 T/Mf 25 P/ Arf vannes r/Ms Z9 vm ne: 4r

y eM/NAL /5 2 r//vf v V0.1. maf 4r 30 MRM/,vu /6 r/Mf i 3/ raf/aMf/vmz fwfaz/:A/cr A caMoA/fA/r ,er auf/ar VA rqM//wus vu 7465 am U l r/Mf @APAC/mf? 7 32 r/Mf TIME l AMM@ W AMA M nn ALMU U U U Unnnmn ,UU U U U UU VUUUAUVU WVM.

l-iS Attorney. l

U U U U UUUUQay/m Patented Mar. 29, 1949 UNITED ySTATES PATENT OFFICE AMPLIFIER CONTROL CIRCUIT Raymond W; Lavender, Johnson City, N. Y., as- I v l signoria General Electric Companyz-a corporation of New lYork 'g Animation octoberis, 1946, serial No. 704,231

`3 claims-.l (o1. 17g-171) f- .'rmslmvention'reiates t amplifier contrciicir-f cuits and it has for an object the-'provisionfoff ai simple, reliable and improved cicuith tllis characterf t More particularly; theinvention relates to de# rivative circuits" and amore speciflcfobject 'of the` invention is the provision Vof a' circuit-of this character which is notfsensitiv'e` to changesin frequency.

A :stm more specific object of l the 'inventan isfthe provision vof an rampliiier"whichL'derives from the periodically varying input'voltage alhalf wave voltage which isan integral plusaderiva-1 tive plus a direct function ofthe input.V

The invention Vis useful in stabilizing follow.'l up control systems of Vwhich the error signal isl a periodically varying voltage.

In carrying the invention`1 into effect in^oner form thereof, the alternating error voltager `is`y supplied toa phase inverter amplifier'valve-l` -The outputcircuit voltage of this valve is coupled to a phase discriminator anda modulator, which con-" Verts the error voltageinto a'half wav'e direct voltage. A capacitor is connected across a'voltage drop device which iscormected in circuitwith thev discriminator; and a feedback circuitis provided from this capacitor to the input circuit `of the" Fora betterand more complete. understanding'f of the invention,` reference should now be' had'to" thefollowing specification andlto the accompany` ing drawing of whichFig.` 1 is a"simple,.schematic l diagram of an embodiment of the invention, and Figs. 2, `3 and 4 are charts of characteristic curves which facilitate an understanding of the in lReferring now to the. drawing;` an electric valve- I is supplied fromy a source of direct voltage which is represented by the terminal-.2 and -ground 3.9v

The terminal -2-is thetpositive supply line'.`r`

shown, the valve l is `provided with an anode Ia,}` l a cathode IbLanda control grid Icq: Included in l the anode circuitof the valvel is a voltage drop:-Y

resistor 5. p i .l

the error voltage; l

A circuit including a phase discriminator 'and-f' sistor 2|. `The phase discriminator andrnodula--' tor is embodiedinfacircular bridge circuit come* prising the secondary Winding of a'transformer IIJ',V resistor II, rectiers I2 and I3 and resistor 14.-

The secondary winding of the transformer is cen`A ter tapped and the two halves of the winding Illav i resistor I4 and rectifier `I3 constitute the fourth arm. Although the rectiers may be of any suitable type they'are preferably of the surface, contact type such for example as the Well known copper oxide rectifier. 'I hey are similarly poled'-` in order to' providethe desired discriminat'orf The primary winding I (lcV of the Ltransformer is* connectedtoa suitable source of reference alternating voltage which has the same frequency* and phase as the error voltage.

In operation the phase" .discriminator andmodulatoractslike aswitch to connect the terminals I5 andV IGevery other half cycle ofthe transformer Voltage. l'Vlfhen the -transformer terminal VIlld is-more positive thanterminali Illey a current willflowaround the loop of thexbridgej inthe direction indicated bythe arrow IIi The center tap of the secondary winding of the transf-l u formerwill beat thesame potential as the center tapof the load circuit at terminal IIL` y'lllhen the terminallllc is more positive than terminal 10d,

currentriiow is prevented by the rectiiiers I3 and,` I2, and theterminals Id and Ille areuisolated.`

The amplifier'is provided vvithfan output cirmodulator circuit.

following description.

Tl'iere is applied to the grid or input circuit off the valve l a signalvoltage which is the sum of any voltagel appearing across capacitor j'I and any voltage induced injthe secondary winding vlafof` i the discriminatorand'mofdulatorbridge andfapr` modulator 8 and a potentiometer resistor 9 is'y coupled by means of capacitor 20 and resistor 2l to" the anode-cathode or outputcircuit *ofthe` valve `I-. The resistance of potentiometer Sil-isv large in 'comparison' with the resistance of re"-Y The resistor I"I 1 cuit which is representedby the conductor I8 and ground. This'output circuit is coupled' by means of'r capacitor I9 to the phasev discriminator and l With the `foregoing understanding of Vthe' ele# L. ments and their organization,v the operation of;l the system will readily beunderstoodjfromthe plied to the terminal I B every other half cycle of the transformer voltage.

The half wave voltage across resistor 9 has a fundamental frequency alternating component, and a direct component as well as some amount of unwanted harmonic Voltage. After a delay the direct component is applied to the capacitor 1 whereas the fundamental frequency is transmitted through the R. C. coupling to the output circuit.

An understanding of the detailed operation is facilitated by considering the grid of the valve I tobe disconnected from the input circuits and to consider the operations that result when alternating voltage signals and direct voltage signals are separately applied between the grid Ic and ground.

If an alternating voltage signal such as represented by the sinusoidal curve 22 is supplied between the grid and ground it is amplified and phase inverted. The amplified voltage is represented by the curve 23 in Fig. 2. This phase inverted amplified voltage is rectified by the phase discriminator and modulator bridge and appears across the resistor 9 as a half wave voltage whichis rep-resented by the curve 24 in Fig. 2. Owing to the R. C. coupling 9, I9, an alternating voltage of fundamental frequency appears at the output terminals I8, 3. This fundamental frequency output voltage is represented by the sinusoidal curve 25 in Fig. 2. The magnitude of the fundamental frequency component is proportional to that of the signal. In addition a direct voltage gradually builds up on capacitor I, of which the polarity and magnitude is represented by the curve 26.

If a direct voltage signal, e. g. an abrupt step of Voltage, as represented by curve 21 of Fig. 3. is separately applied to the grid Ic, the valve I produces at its anode terminal a faithful but amplified and inverted replica as represented by curve 28 in Fig. 3. However, owing to the capacitor 20 this voltage is transmitted as a decrement or surge to the input terminal I of the phase discriminator and modulator. It is represented by the curve 29 in Fig. 3.

Owing to the periodic rectifying action of the phase discriminator the voltage at the output terminal I6 of the Imodulator, appears as a series of voltage pulses of which the envelope has the same general shape as the surge voltage 29 at the bridge input terminal I5. The voltage at the terminal I6 is represented by the curve 30. Owing to the R. C. coupling this voltage produces at the output terminals 3 and I8 a voltage of fundamental frequency and of decreasing amplitude as represented by the curve 3l in Fig. 3. The direct component of the voltage at the output terminal I6 of the phase discriminator is applied to the capacitor 'I and the voltage across the capacitor builds up at first and ,then decays in a manner Which is illustrated by the curve 32.

In the complete circuit, i. e., with the grid I c of the valve connected to the signal input circuit, both of the operations described in the foregoing are taking place simultaneously, for an alternating error voltage applied to the terminals of the primary winding of the error input transformer 5 soon produces a direct component on capacitor 'I, and a direct component on the capacitor produces an alternating output which opposes the eifect of the original alternating voltage signal.

For example, consider that an alternating error signal -voltage of constant magnitude such as.

represented by curve 33 of Fig. 4 is suddenly applied to the input terminals of the error input transformer 6. The direct component of voltage of negative polarity which builds up on the capacitor 'I as represented by curve 34 is applied to the grid Ic. The total signal voltage applied to the grid is represented by the sinusoidal curve 35 of which the axis has the same general form as the median line of the curve 34.

The direct voltage which builds up on the capacitor 'I and which is applied to the grid I c as a component of the total signal is amplified, phase inverted and passed as a surge through coupling capacitor- 20 to the discriminator and modulatorinput terminal I5. This phase inverted surge voltage is indicated by the dotted curve 36 in Fig. 4. Similarly the alternating component of the signal voltage is phase inverted, amplified and transmitted to the discriminator input terminal, so that the total voltage appearing at the terminal I5 is Arepresented by the sinusoidal curve 3'I.

At the output terminal I6 of the discriminator there appears a half wave voltage, the characteristics of which are represented by the curve 38 in Fig. 4. This rectied and modulated voltage after passing through the R. C. coupling 9, I9 appears at the output terminals 3 and I8 as an alternating Voltage of fundamental frequency as indicated by the sinusoidal curve 39. The magnitude of the direct component of the grid signal voltage` is such that the magnitude of the voltage' at the output terminals 3 and I8 is; at first, reduced as indicated by the diminishing amplitude of the alternations of the curve 39 between the points 39a and 39D. As time proceeds, as indicated by the succession of cycles, the direct component voltage on the capacitor 'I tends to remain constant or decrease slightly, and consequently 40 the direct component voltage across the resistor In the operation described in the foregoing the voltage fed back by the capacitor 1 to the input circuit is a first derivative function of the voltage at the terminal I6. The capacitor 20 supplies a voltage to the input of the modulator which is an integral function of the signal voltage.

Thus the output voltage 39 contains an integral function plus a derivative function plus a directfunction. Although in accordance with the provisions of the patent statutes this invention is described as embodied in concrete form and the principle thereof has been explained together with the best mode in which it is now contemplated applying that principle, it will be understood that the apparatus shown and described is merely illustrative and that ,the invention is not limited thereto since alterations and modications will readily suggest themselves to person-s skilled in the art .without departing from the true spirit of the invention or from the scope of ,the annexed claims. I' -1 What I claim as new and desire to secure by Letters Patent of the United States, is:

1. An amplifier comprising an electric valve provided with an anode-cathode circuit and a control grid input circuit, means for supplying to said grid circuit a periodically varying voltage, a third circuit having a resistance-capacitance coupling to said anode-cathode circuit, a phase discriminator and modulator bridge and a voltage drop device connected in said third circuit, said bridge comprising a transformer having a primary winding energized with a periodically varying reference voltage having the same frequency and phase as said input circuit voltage and a secondary winding constituting two arms of said bridge, an output circuit, a capacitative coupling for supplying the alternating component of the voltage transmitted by said bridge to said output circuit, a capacitor connected in parallel with said voltage drop device to be charged by the direct component of the voltage transmitted by said bridge and a feedback circuit from said capacitor to said input circuit.

2. An amplier comprising an electric valve provided with an anode-cathode circuit and a control grid input circuit, means for supplying to said grid circuit a periodically varying voltage, a periodically varying reference voltage having the same frequency and phase as said grid circuit voltage, a third circuit having a resistance capacitance coupling to said anode-cathode circuit and including a phase discriminator and modulator ydevice energized from said reference voltage for rectifying said anode-cathode circuit voltage and a voltage drop device connected in circuit with said discriminator device, a capacitor connected in parallel with said volt- .;age-rdrop device to be charged by said rectified voltage, a feedback circuit from said capacitor to said grid input circuit, an output circuit, and a capacitance coupling said third circuit to said output circuit for transmitting the alternating component of said rectied Voltage to said output circuit.

3. An amplier comprising an electric Valve provided with an anode-cathode circuit and a control grid input circuit, means for supplying to said grid circuit a periodically varying voltage, means for rectifying the voltage of the anodecathode circuit comprising a phase discriminator and modulator bridge comprising a transformer having a secondary winding constituting two arms of the bridge and a primary winding, means for supplying to said primary winding a periodically varying voltage having the same frequency and phase as said grid voltage, a third circuit comprising said secondary winding and a voltage drop device having a resistance capacitance coupling to said anode-cathode circuit, a capacitor connected in parallel with said voltage drop device to be charged by said rectified voltage, a feedback circuit from said capacitor to said grid circuit and an output circuit having a capacitance coupling to said third circuit.

RAYMOND W. LAVENDER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,398,025 Campbell Nov. 13, 1945 2,399,675 Hays, Jr May '7, 1946 

